Eyes & Ears Flashcards
What are the 2 parts of the fibrous coat?
- sclera
2. cornea
What are the three layers of the eyeball?
- fibrous coat (homologous to dura)
- vascular coat (homologous to arachnoid & pia)
- nervous coat (homologous to CNS)
What is the sclera?
-dense, white CT into which the extrinsic eye muscles insert
What is the cornea?
- continuous with the sclera, but transparent to allow light to project to retina
- most of the refraction of the light
- avascular, draws nutrients from aqueous humor by diffusion
What are the constituents of the anterior, external eye?
- eyebrow
- superior palpebral sulcus
- upper eyelid
- pupil
- caruncula lacrimalis
- lateral angle of eye
- medial angle of eye
- bulbar conjunctiva
- posterior border of eyelid
- anterior border of eyelid
- iris
- lower eyelid
- lateral palpebral commissure
What is conjunctiva?
- conjunctiva is a thin, clear mucus membrane
- covers the anterior, external part of the eye & lines internal parts of both eyelids
What does the conjunctiva produce?
-conjunctiva + lacrimal gland produce fluid that bathes the anterior surface of the eye= keeps it moist & nourished
What is MALT?
- mucosa-associated lymphatic tissue
- found w/in conjunctiva as well as immunoglobulins which it secretes
What does the vascular coat consist of?
- blood vessels
- choroid & structures
- ciliary body which regulates the refraction of light
What is the choroid?
-layer of numerous anastamosing blood vessels
What does the ciliary body do?
- controls the shape of the lens–> change refractory index
- helps with production of aqueous humor
What does the iris do?
controls pupil size
The iris has how many sets of muscles & what does each do?
- 2 sets; control pupil size
1. sphincter pupillae
2. dilator pupillae
What is the sphincter pupillae innervated by?
-parasympathetic fibers from the Edinger-Westphal nucleus that travels along the oculomotor n. & decreases pupil size
What is the dilator pupillae innervated by?
-innervated by sympathetic nerves from the superior cervical ganglion & increases pupil size
What does the cornea cover? What is it innervated by? What are the parts which make it up?
- iris, pupil & anterior chamber
- accounts for 2/3 of eyes optical (refractory) power
- sensory innervation by trigeminal nerve (CN V)
- multilayered structure consisting of epithelium, collagen & endothelium
What makes up the lens? What about optical power? What happens with age?
- composed of stiff elongated prismatic cells known as lens fibers
- less optical power than cornea, but adjustable by ciliary muscles (accommodation- eyes change due to image coming close to face) (flex to make flat, relax to make round)
- elasticity of the lens decreases with age= more difficult to focus on objects close to the eye (prebyopia)
What is in the anterior chamber?
-aqueous humor, ultrafiltrate of blood
What does the aqueous humor provide? Where does it come from? Where does it drain?
- nutrition and assists in immune response
- from ciliary body
- drains through canal of Schlemm
What happens with an overproduction/underproduction of aqueous humor?
-can cause a build up of aqueous humor & increased P in the anterior chamber–> this is what happens in glaucoma & blindness results from damage to the optic n.
What does the nervous coat consist of?
-consists of retina
What is the retina?
- pigmented receptors & neurons that convey light information to ganglion cells
- ganglion cells send axons centrally to the optic disc & forms the optic n.
What is the retina? What does it contain?
- multilayered inner lining of the eye
- contains rods & cones, the photo-sensitive cells of the eye
- highest density of cones are in the macula densa (macula lutea & fovea centralis)
What are rods & cones? What do they respond to? What are they responsible for?
- rods are more numerous than cones & more sensitive to light
- rods do not respond to red light
- cones detect color & provide acute vision; 3 types: red, blue, green
- both rods & cones require protein retinal (metabolite of vit. A)
The optic nerve/tract is an extension of what? What are its characteristics?
THE BRAIN
-is a CNS structure & should be a ‘tract’
What surround the nerve & up to where?
meninges surrounds the nerve up to the sclera
What two things extend to the lamina cribrosa?
subarachnoid space with CSF extends to lamina cribrosa
Ganglion cells are like what?
-CNS neurons
What are the two cells specific to the CNS for myelination?
- oligodendrocytes myelinate the axons
- astrocytes surround cell bodies & dendrites
What is papilledema?
- one of 1st signs of increased intercranial P
- increased CSF P limits venous return from retina & causes edema under optic disc
- ophthalmoscopic view shows blurred disc margins where the optic disc is raised
What is the vitreous body/humor?
- clear, gel-like fluid
- 98, 99% H2O
- contains hyaluronic acid & type II collagen fibrils that are slowly replaced
- sits up against retina, supporting the spherical shape of the globe & keeping the retina in place
What is the hyaloid canal?
- vestige of hyaloid artery used to nourish embryonic lens
- blood & cell debris removed by local phagocytes, but residual pieces of hyaloid artery remain as a type of floater
What are floaters?
- visual specks or clouds formed by tiny separated clumps of gel in the vitreous body that are too large to be phagocytized
- born w/the # of floaters you will have
How does retinal detachment occur?
-too little vitreous humor= doesn’t support eye= pulls away from retina
What is the visual pathway? light transformed into what? by what? travel to where?
- light hitting the retina is transformed into nerve impulses by the rods & cones
- impulses travel through the optic n. to the optic chiasm
- from optic chiasm, these signals travel to lateral geniculate body of the thalamus
- after the lateral geniculate, signals travel through the optic radiations to the primary visual cortex of the occipital lobes
What is the abducens n. responsible for innervating and what does that muscle do?
lateral rectus- abducts the eye (lateral gaze)
What does the trochlear n. innervate? What does this muscle do?
superior oblique- internally rotates, depresses & abducts the eye (down & out)
What does the oculomotor n. innervate?
inferior oblique, medial rectus, superior rectus & inferior rectus AS WELL as the ciliary body
What are the 3 parts of the ear?
external, middle & inner ear
What makes up the external ear? What are these structure for? What glands are there, what do they produce & what are they good for?
- pinna (outer ear structure) & auditory meatus
- these structures boost sound wave P & funnel it to the tympanic membrane
- modified sebaceous glands line the external auditory meatus; create ear wax (cerumen)
- ear wax protects the ear from irritation & infection
Where is the middle ear (b/w what 2 structures)?
- internal to tympanic membrane & external to oval window
- ossicles are w/in middle ear
What are the 3 ossicles of the middle ear? What kind of joint?
- malleus: attaches to tympanic membrane distally & the incus proximally
- incus: connects the malleus to the stapes
- stapes: attaches to the oval window of the inner ear
- articulations between ossicles are synovial joints
Where does the auditory tube drain to?
middle ear into the nasopharynx
What does the tensor tympani attach to? What does the stapedius attach to? What are they for?
- tensor tympani to malleus
- stapedius to the stapes
- both contract to reduce movement of the ossicles & protect ear from excessive noise
What are the parts of the inner ear? What is it innervated by?
- cochlea, vestibule & semicircular canals
- innervated by vestibulococchlear n.
What does the stapes do in relation to the cochlea?
- movement of stapes at the oval window moves the perilymph (w/in the cochlea) in the scala vestibuli
- this movement vibrates the endolymph in the scala media (cochlear duct), the basilar membrane & the Organ of Corti
- movement of the hair cells of the Organ of Corti is converted to electric signals that travel along the vestibulocochlear n.
What is the auditory pathway? What does it relay?
- cochlear divison of the vestibulocochlear n. transmits n. impulses first back to its nucleus (the cochlear nucleus) then to the superior olivary nucleus
- relays processed info; this processed info ascends to the inferior colliculus before being transmitted to the thalamus
- from the thalamus this info is sent to the primary auditory cortex (in the temporal lobe)
What system is responsible for balance?
- vestibular system (equilibrioception)
- visual system tells us where we are with respect to the external environment
- P & proprioceptors, which tell us about position of our bodies
What does the vestibule contain? What are these structures filled with/what do they have? What sits on top of the hair cells?
- saccule, uricle & 3 semicircular canals
- filled with fluid (endolymph)
- all also have hair cells that when moved by gravity or motions of the head, generate n. impulses
- otoliths (crystalline structures composed of gelatinous matrix & calcium carbonate) attach to the hair cell; amplify the effects of gravity or movement to activate the hair cells
What are the semicircular canals made up of? What is at the base of each canal?
- 3 hemicircular structures of bone, lined with periosteum & contain endolymph
- horizontal, superior & posterior semicircular canals correspond roughly to the 3 planes of 3D space
- at base of each canal is an enlargement (ampulla); as head and/or body moves, endolymph movement lags behind slightly, deforming the ampulla= hair cells in ampulla are affected by this movement which triggers n. impulses
What is BPPV? What is it caused by?
- Benign Paroxysmal Positional Vertigo: condition which the pt is overcome by a sudden sensation of spinning
- thought to be due to disturbance of inner ear, in which otoliths from the saccule or utricle enter the semicircular canals & activate hair cells
- diagnosis is based on pt history & Dix-Hallpike maneuver (the roll test)
- treated with the Epley maneuver or Semont maneuver
